PSC 833 (valspadar) is a non-immunosuppressive and non-nephrotoxic cyclosporin analogue which is a potent inhibitor of the multidrug resistance transporter, P-glycoprotein. P-glycoprotein is expressed in 70 to 80% of colon cancers and may be an important mechanism of resistance to paclitaxel. The goal of this study is to assess the remission rate of the combination of paclitaxel and PSC 833 in this type of cancer. Seven patients have been enrolled to date, with a target of between 19 and 30 patients total over the next two years. No data are yet available.